When the transmission goes bad on a car, it's time to get a new vehicle because a new transmission could be more costly than purchasing another vehicle.

For the best vehicle maintenance, the automatic transmission oil and filter should be changed every 30,000 miles unless the vehicle is filled with an automatic transmission fluid from Dexron III fluid, which is good for at least 100,000 miles.

The automatic transmission creates internal friction, including the friction of the fluid on the inside of the torque converter, the friction created when the clutch plates engage and the normal friction created by gears and bearing carrying their loads.

When the vehicle is in motion, it doesn't take long for the parts under the hood to create a dangerous amount of heat, potentially reaching temperatures of 175 degrees under normal driving conditions. A temperature of 175 degrees is the normal amount of heat that transmission fluids are designed to operate. If the temperature stays consistent throughout the life of the vehicle, reaching 100,000 miles without changing the transmission fluid is possible, but when temperatures reach degrees higher than 175, it speeds up the life of the fluid.

Once temperatures under the hood reach elevated operating temperatures, the automatic transmission fluid oxidizes, turns brown and begins to emit a smell similar to burnt toast. The high temperatures destroy the quality of the fluid's lubrication and its friction characteristics. Varnish will also begin to form on internal parts, interfering with the process of the transmission operating.

If the vehicle overheats and the temperature elevates above 250 degrees, the rubber compounds under the hood begin to harden, which can lead to leaks, pressure losses and other problems that could prove to be more taxing on the entire vehicle. The transmission may also begin to slip at high temperatures, only increasing the heat and causing the clutch to burn out and the transmission to stop working completely.

An overhaul of the transmission and any other parts that were affected by the overheating will be necessary, which is estimated at $1,500 or more on a late model front-wheel car or minivan.

According to automotive experts, every 20 degrees a transmission increases above 175 degrees, the automatic transmission fluid's life is cut in half.

What causes a vehicle to overheat
Several factors may increase the temperature of the automatic transmission fluid. Several of the factors include towing a trailer, mountain driving, driving at consistently high speeds during hot weather, stop-and-go driving in city traffic and rocking an automatic transmission from drive to reverse to free a vehicle from mud, snow or other weather conditions.

What fluid should be used
Auto owners often neglect to read the owner's manual when they purchase a car, but the book contains the blueprint to getting the most use out of a car. Included in the owner's manual is the kind of gas needed to maximize the life of the vehicle, the automatic transmission fluid to use and other maintenance tips.

The transmission could also have the type of fluid needed on the dipstick. Using the wrong type of fluid could have a detrimental effect on a vehicle, which could also result in the vehicle not driving as well as it did when it was taken off the dealer's lot.